Graphical display devices having a wide field of view (FOV) have been developed. Such devices include head mounted display (HMD) devices. Typically in an HMD device, a small display device is worn on a user's head. The display device has a display optic in front of one eye (monocular HMD) or each eye (binocular HMD). An HMD device typically includes sensors that can sense the orientation of the device and change the scene shown by the display optics as the user's head moves. Conventionally, most stages of rendering scenes for wide FOV displays are performed by planar rendering where all parts of the screen have the same number of pixels per unit area.
However, rendering for virtual reality (VR) programs, which is often performed in conjunction with HMD devices, requires a higher frame rate than conventional flat screen rendering to prevent a user from experiencing motion sickness. HMD for VR has optical systems to show rendered scenes in wide FOV for immersive experiences. While screen area around a primary gaze point (sometimes called the foveal region) requires high resolution, the areas outside the primary gaze point are observed only by the peripheral vision and can therefore be rendered at a lower resolution, or may contain less detail. Such rendering is sometimes referred to as foveated rendering.
Research has been performed that seeks to apply foveated rendering at the pixel level by selectively adjusting the pixel resolution for different parts of the screen. See co-pending U.S. patent application Ser. No. 14/246,066, to Mark Evan Cerny, filed Apr. 5, 2014, which is incorporated herein by reference. Furthermore, the foveated rendering concept may be applied at earlier stages of a graphics processing pipeline, such as the geometry level, e.g., by adjusting the tessellation of computer generated objects for different parts of the screen on which they are displayed. See co-pending U.S. patent application Ser. No. 14/927,157 to Jun Murakawa et al. filed Oct. 29, 2015, which is incorporated herein by reference. These approaches, and others, can reduce the computational load on graphics processing hardware by concentrating computational resources on rendering more important parts of an image on a display.
It is within this context that the present disclosure arises.